<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<h1>
    每一次的点击都会有一个警告框
</h1>
<hr>
<p>
    <button onclick="functionForHello()">
        start after click me!
    </button>
</p>

<script>
    function functionForHello() {
        setInterval(function () {
            alert("Hello!")
        }, 3000)
    }
</script>
</body>
</html>